This invention relates to multiple spindle machines, and particularly to multiple spindle machines having plural machining capability.
Multiple spindle machines are known in the prior art. Multiple spindle machines are used to mass produce standardized types of components. Multiple spindle machines typically have several workstations at which machining operations are performed. A piece of raw stock, such as bar stock, enters the machine at a first station and as the machine indexes, various machining operations are performed. Once a station is indexed completely through the machine a completed a part is formed. The part is released and the process is repeated for that station with a new piece of raw stock. The advantage of multiple spindle machines is that all stations in the machine are producing parts simultaneously, resulting in high production.
Multiple spindle machines typically have a large indexing drum with four, six or eight stations thereon. Each of the stations carries a work piece. In all but one of the stations, where a new piece of stock enters, a machining operation is performed. After each operation is completed the drum is rotated so that each work space moves sequentially through the location where the various operation is performed. Machining operations typically performed at a multiple spindle machine include turning and threading.
Most multiple spindle machines are very efficient in terms of producing standardized parts at a high rate. However, one draw back associated with multiple spindle machines is that the entire machine often operates off of a single main motor. The main motor simultaneously drives all the devices in the machine.
The speed of the multiple spindle machine typically changes from high speed to low speed and back again during the course of the operating cycle. High speed is typically used for times in the machine cycle where critical machining operations are not occurring. High speed operation is desirable when the machines are indexing or when the tools are moving to or away from the work pieces that are not performing work thereon. Low speed operation is used when the tools in the machine are forming the metal. As stated, the machining operation of the bar stock is performed utilizing a threading die which is driven via a worm gear. In typical multiple spindle machines a worm gear is driven through a threading clutch. The threading clutch acts to translate rotation from a reversible shaft to the threading shaft.
As previously described a typical prior art multiple spindle machine includes a main drive motor which operates all of the components on the multiple spindle machine that perform machining operations on the work pieces through a transmission.
The transmission includes various components including a high speed clutch and a low speed clutch. A rear view of a typical multiple spindle machine set up for a dual threading operation is shown in FIG. 1 and has a high speed clutch 12 and a low speed clutch 14. FIG. 2 is a side view of the multiple spindle machine shown in FIG. 1.
A high speed clutch shaft 11 extends along a longitudinal direction in operative connection with a main motor (not shown) of the multiple spindle machine and may be rotated in either a first or second direction to drive high speed clutch 12 in either the first or second direction. A low speed clutch shaft 13 extends along a longitudinal direction in operative connection with the main motor and may be rotated in either a first or second direction to drive low speed clutch 14 in either the first or second direction.
Work pieces formed in the multiple spindle machine are carried on six stations 20 located on a main spindle carrying drum (not shown), two of the six stations 20 being utilized for threading operations in this set up, which will be described below without reference to the other machining operations.
The high and low speed clutches are selectively actuated to drive through a gear train 15 first shaft 16 and second shaft 36 at either a high or a low speed. High speed is used when machining operations are not occurring, such as when the machine is indexing or when the tools are moving to or away from the work pieces. Low speed operation is used when the tools in the machine are machining the work piece.
Stations consist of rotatable spindles through which work piece stock, such as bar stock, extends. Raw stock enters the machine at a first position then indexes through each of the other five stations so that a completed part is produced and cut off before the drum returns to the first position.
A station 20 is schematically shown holding a work piece 22 in FIG. 3. Similarly a second station 20 holds a second work piece 23 as shown in FIG. 3A. The work pieces are held in collets in the spindle and rotate in the direction of the arrow as shown. When the low speed clutch 14 is engaged, the output shafts 16, 36 will rotate in the same direction as the work pieces. The high speed clutch 12 is engaged once the threads-have been formed. The threading tool is then backed off the work piece.
The threading process for the first threading tool is illustrated schematically in FIGS. 3-4. A first threading tool 24 is guided on a first slide 26. A switch actuator 30 is attached to the threading tool 24. The first threading tool is shown in the fully retracted position shown in FIG. 3. The switch actuator engages a limit switch 32 so as to indicate that the first threading tool is in the fully retracted position. As the multiple spindle machine cycles, first threading tool 24 is moved to engage first work piece 22 by movement on first slide 26 using an actuator such as first pneumatic cylinder 28. The threading tool moves to engage the work piece until the limit switch 32 is moved to the fully forward, full stroke position by the switch actuator 30 as shown in FIG. 4.
The threading process for the second threading tool is illustrated schematically in FIGS. 3A-4A. A second threading tool 40 is guided on a second slide 42. As the multiple spindle machine cycles, second threading tool 40 is moved to engage second work piece 23 by movement on second slide 42 using an actuator such as a second pneumatic cylinder 44. The second threading tool moves to engage the second work piece until limit switch 32 has moved to the fully forward, full stroke position of first threading tool 24 by the switch actuator 30 as shown in FIG. 4.
When first threading tool 24 has been moved to the fully forward position as shown in FIG. 4, the actuator 30 changes direction in response to control signals to return the first and second threading tools to their original positions. The switch actuator 30 engages the limit switch 32 to indicate that the first threading tool 24 is again in the fully retracted position as shown in FIG. 5, the threading operation is complete and the threading tools are sufficiently disposed from the work pieces and spindle so that the main drum may index.
The second threading tool 40 does not have a switch actuator to engage a limit switch so as to indicate that the second threading tool is in either the fully forward or the fully retracted position. The multiple spindle machine is set up based on both threading operations being completed simultaneously. Use of a second limit switch and switch actuator combination would be redundant when the machine operates correctly. Also, unintended operation could occur if a second actuator and switch combination sent a completion signal rather than the first. A flow diagram of the threading operation is shown in FIG. 6.
All of the stations rotate the work pieces in the same direction and all of the machining operations occur generally simultaneously. There are several problems associated with the design and operation of the prior art multiple spindle machines in which threading simultaneously at a plurality of stations has been attempted. Threading operations must be started and finished generally simultaneously with each other and with the other machining operations so that all start and finish simultaneously with each other and the other operations for the drum to index to the next position. As described above, only one limit switch 32 is used to indicate that both threading tools 24, 40 are in the fully forward, full stroke position. The machine operator must set up the switch actuator 30 and limit switch 32 so that threading tools 24, 40 have completed their threading operations when the switch is activated.
Electromagnetic clutches have been used as the high and low speed clutches to obtain improved synchronization, but they provide sufficient torque only to tap threads in small stock of soft materials such as aluminum or brass. A problem occurs with a lack of static torque capacity produced by the electromagnetic clutches. Replacing electromagnetic clutches with pneumatic clutches increases torque by approximately 50%, thereby increasing plural threading capability. However, a problem occurs with pneumatic clutches in that the threading operations is more difficult to synchronize sufficiently. Long set up times are common, resulting in lost production time and generation of unusable scrap pieces.
Thus there exists a need in for a multiple spindle machine with plural threading capability which reliably simultaneously and synchronously threads bar stock of desired material and size.
The object of the present invention is to provide a multiple spindle machine plural machining apparatus and method.
A further object of the present invention is to provide a multiple spindle machine plural machining apparatus and method in which the torque capacity is sufficient to facilitate the use of plural machining tools.
A further object of the present invention is to provide a multiple spindle machine plural machining apparatus and method in which the machining tools which finish their operations idle until the last tool finishes its operation.
A further object of the present invention is to provide a multiple spindle machine plural machining apparatus and method which reduces the need for precisely coordinated machine settings and reduces machine set up time.
A further object of the present invention is to provide a multiple spindle machine plural machining apparatus and method which reduces material stock waste during machine set up.
A further object of the present invention is to provide a multiple spindle machine plural machining apparatus and method which can be retrofit to existing multiple spindle machines.
Further objects of the present invention will be made apparent from the following Best Modes for Carrying Out Invention and the appended claims.
The foregoing objects are accomplished in the preferred embodiment of the present invention by a plural machining apparatus and method for a multiple spindle machine.
The invention has alternative embodiments, each permitting increased torque and independent thread tapping at low speed followed by simultaneous withdrawal at high speed of the taps from the work piece.
In the first embodiment the machining attachments are pneumatic threading clutches at two of the stations of the multiple spindle machine. The threading clutches operatively engage threading tools at low speed to tap work pieces. When the first tool has reached its fully forward, full stroke position, its pneumatic clutch disengages to allow its tool to idle until the second tool has reached its fully forward, full stroke position, whereupon its pneumatic clutch disengages and signals a high speed clutch to engage and withdraw both tools.
In the second embodiment separate servo motors at two stations each rotate threading tools. When the first threading tool has reached its fully forward, fill stroke position, its servo motor idles until the second tool has reached its fully forward, full stroke position, and signals for withdrawal of both tools.
The plural threading apparatus and method further comprises a limit switch and switch actuator combination for each threading tool to signal completion of the threading operation.
The plural threading apparatus and method further comprises a controller to determine when threading is complete.